WO2012023331A1 - Optical film, polarizing plate, and liquid crystal display device - Google Patents

Abstract

The purpose of the present invention is to provide: an optical film through which the leakage of light rarely occurs and which has good adhesion to a polarizer; a polarizing plate; and a liquid crystal display device. This optical film comprises (A) an acrylic resin and (B) a cellulose ester resin at a ratio of 95:5 to 50:50 by mass, and is characterized in that the acrylic resin (A) is represented by general formula (1) and has a weight average molecular weight (Mw) of 20000 to 1000000 inclusive. General formula (1): -(MMA)p-(X)q-(Y)r- [In the formula, MMA represents a methyl methacrylate; X represents a monomer unit copolymerizable with a MMA and having at least one group selected from a secondary amino group, a tertiary amino group, a phthalimide group; an α, β-saturated ester group and an ether group; Y represents a MMA or a monomer unit copolymerizable with X; and p, q and r are expressed by mass% and fulfill the requirements represented by the following formulae 50≤p≤99, 1≤q≤ 50 and p+q+r = 100.]

Description

Optical film, polarizing plate, and liquid crystal display device

The present invention relates to an optical film, a polarizing plate, and a liquid crystal display device, and more particularly to an optical film, a polarizing plate, and a liquid crystal display device that do not deteriorate heat resistance over time.

Demand for liquid crystal display devices is expanding for applications such as liquid crystal televisions and personal computer liquid crystal displays. In general, a liquid crystal display device is composed of a liquid crystal cell in which a transparent electrode, a liquid crystal layer, a color filter, etc. are sandwiched between glass plates, and two polarizing plates provided on both sides thereof. The optical element (polarizing plate protective film) is sandwiched between a child (also referred to as a polarizing film or a polarizing film). As this polarizing plate protective film, a cellulose triacetate film is usually used.

However, due to recent technological advances, the increase in size of liquid crystal display devices has accelerated, the amount of light from the backlight has increased, and heat resistance in the liquid crystal display devices has become a problem, and improvements have been demanded.

A method for improving heat resistance by mixing an acrylic resin and a cellulose resin has been proposed (Patent Documents 1, 2, and 3).

However, the heat resistance after long-term use was still insufficient.

International Publication No. 2009/047924 JP 2009-1744 A JP 2009-179731 A

In view of the above problems, an object of the present invention is to provide an optical film, a polarizing plate, and a liquid crystal display device that improve heat resistance over time.

The above object of the present invention can be achieved by the following configuration.

1. In an optical film containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 50:50, the acrylic resin (A) is represented by the following general formula (1), and has a weight average molecular weight. Mw is 20000 or more and 1000000 or less, The optical film characterized by the above-mentioned.
General formula (1)
-(MMA) p- (X) q- (Y) r-
[Wherein, MMA is copolymerized with methyl methacrylate, X is copolymerized with MMA having at least one group selected from hydroxyl group, secondary amino group, tertiary amino group, phthalimide group, α, β-saturated ester group and ether group] Y represents a monomer unit that can be copolymerized with MMA and X. p, q, and r are% by mass, and 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100. ]
2. 2. The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is 2.0 or more and 3.0 or less, and the substitution degree of the acyl group having 3 or more and 7 or less carbon atoms is 1.2 or more. 2. The optical film as described in 1 above, wherein the cellulose ester resin (B) has a weight average molecular weight Mw of 75,000 or more and 300,000 or less.

3. The said optical film contains 0.5 mass% or more and 30 mass% or less of acrylic particle (D) with respect to the gross mass of resin which comprises this optical film, Said 1 or 2 characterized by the above-mentioned. Optical film.

4. 4. A polarizing plate comprising the optical film described in any one of 1 to 3 above.

5. 4. A liquid crystal display device comprising the optical film described in any one of 1 to 3 above.

The present invention provides an optical film that improves heat resistance over time, thereby providing a polarizing plate and a liquid crystal display device using the optical film.

It is the figure which showed typically the process of the solution casting film forming method preferable for this invention.

Hereinafter, the best mode for carrying out the present invention will be described in detail.
<Optical film of the present invention>
The optical film of the present invention is an optical film containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 50:50, and the acrylic resin (A) is represented by the following general formula ( 1), wherein the weight average molecular weight Mw is 20,000 or more and 1,000,000 or less.
General formula (1)
-(MMA) p- (X) q- (Y) r-
[Wherein, MMA can be copolymerized with methyl methacrylate, and X can be copolymerized with MMA having at least one group selected from secondary amino group, tertiary amino group, phthalimide group, α, β-saturated ester group, and ether group. Y represents a monomer unit copolymerizable with MMA and X. p, q, and r are% by mass, and 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100. ]
<Acrylic resin (A)>
The acrylic resin used in the present invention includes a methacrylic resin.

The acrylic resin (A) of the present invention is represented by the following general formula (1), and has a weight average molecular weight Mw of 20,000 to 1,000,000.
General formula (1)
-(MMA) p- (X) q- (Y) r-
[Wherein, MMA represents methyl methacrylate, X represents a group selected from a secondary amino group, a tertiary amino group, a phthalimide group, an α, β-saturated ester group, and an ether group (hereinafter abbreviated as a functional group). Y represents a monomer unit copolymerizable with MMA and X, and represents a monomer unit copolymerizable with at least one MMA. p, q, and r are% by mass, and 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100. ]
X is a vinyl monomer copolymerizable with MMA, and X may be one type or two or more types, and one monomer unit may have a plurality of functional groups.

Specific examples of X include the following monomers. Examples of the monomer having a secondary amino group include tetramethylpiperidyl methacrylate, and examples of the monomer having a tertiary amino group include pentamethylpiperidyl methacrylate, dimethylaminoethyl methacrylate, and dimethylaminoethyl acrylate.

Examples of the monomer having a phthalimide group include N-acryloyloxyethylhexidophthalimide.

Examples of the monomer having an α, β-saturated ester group include 2-acryloyloxyethyl succinate, 2-methacryloyloxyethyl succinate, and γ-butyrolactone acrylate.

Examples of the monomer having an ether group include 2-ethylhexyl polyethylene glycol acrylate, methoxy polyethylene glycol methacrylate, methoxy triethylene glycol acrylate, nonylphenoxy polyethylene glycol acrylate, 4-hydroxybutyl acrylate glycidyl ether, tetrahydrofurfuryl acrylate, oxetane acrylate, ethyl carbide. Examples include tall acrylate.

These monomers are commercially available.

Q is 1 ≦ q ≦ 50 and is appropriately selected depending on the properties of the monomer, but preferably 5 ≦ q ≦ 30. X may be a plurality of monomers.

The monomer X contributes to the improvement of heat resistance because the functional group has an electron loan pair and coordinates the water molecule, thereby causing the retardation of the optical film generated over time. It is speculated that the crystal orientation of a certain resin may be suppressed.

Also, since many functional groups are non-dissociable, it is considered that the acid is not generated due to decomposition over time and is physically stable.

Y in the acrylic resin (A) of the present invention represents a monomer unit copolymerizable with MMA and X.

Examples of Y include monomers described in Patent Documents 1, 2, and 3, such as acrylic monomers other than MMA, methacrylic monomers, olefins, acrylonitrile, styrene, and vinyl acetate. Y may be two or more.

Y can be used as needed and is most preferably not used.

The acrylic resin (A) of the present invention has a weight average molecular weight (Mw) of 20000 or more from the viewpoint of improving transparency particularly when it is compatible with the cellulose ester resin (B).

The weight average molecular weight (Mw) of the acrylic resin (A) is more preferably in the range of 20,000 to 1,000,000, particularly preferably in the range of 100,000 to 600,000, and most preferably in the range of 150,000 to 400,000. preferable.

The upper limit value of the weight average molecular weight (Mw) of the acrylic resin (A) is preferably 1000000 or less from the viewpoint of production.

The weight average molecular weight of the acrylic resin of the present invention can be measured by gel permeation chromatography. The measurement conditions are as follows.

Solvent: Methylene chloride Column: Shodex K806, K805, K803G (Used by connecting three Showa Denko Co., Ltd.)
Column temperature: 25 ° C
Sample concentration: 0.1% by mass
Detector: RI Model 504 (manufactured by GL Sciences)
Pump: L6000 (manufactured by Hitachi, Ltd.)
Flow rate: 1.0ml / min
Calibration curve: Standard polystyrene STK standard polystyrene (manufactured by Tosoh Corp.) Mw = 2,800,000-500 calibration curves with 13 samples were used. The 13 samples are preferably used at approximately equal intervals.

As the method for producing the acrylic resin (A) in the present invention, any known method such as suspension polymerization, emulsion polymerization, bulk polymerization, or solution polymerization may be used. Here, as a polymerization initiator, a normal peroxide type and an azo type can be used, and a redox type can also be used.

The polymerization temperature may be 30 to 100 ° C. for suspension or emulsion polymerization, and 80 to 160 ° C. for bulk or solution polymerization. In order to control the reduced viscosity of the obtained copolymer, polymerization can be carried out using alkyl mercaptan or the like as a chain transfer agent.
<Cellulose ester resin (B)>
The cellulose ester resin (B) of the present invention has a total acyl group substitution degree (T) of 2.0 to 3.3 from the viewpoint of transparency particularly when it is improved in brittleness and is compatible with the acrylic resin (A). The substitution degree of the acyl group having 0 and 3 to 7 carbon atoms is preferably 1.2 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is preferably 2.0 to 3.0. .

That is, the cellulose ester resin of the present invention is a cellulose ester resin substituted with an acyl group having 3 to 7 carbon atoms. Specifically, propionyl, butyryl and the like are preferably used, but a propionyl group is particularly preferably used. .

When the total substitution degree of the acyl group of the cellulose ester resin (B) is less than 2.0, that is, when the residual degree of the hydroxyl groups at the 2, 3, and 6 positions of the cellulose ester molecule is more than 1.0, the acrylic ester When the resin (A) is not sufficiently compatible with the resin (A) and used as an optical film, haze becomes a problem.

Even if the total substitution degree of the acyl group is 2.0 or more, if the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2, sufficient compatibility cannot be obtained.

For example, even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 2 carbon atoms, that is, the acetyl group is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1. When it is less than 2, the compatibility is lowered and the haze is increased.

Even when the total substitution degree of the acyl group is 2.0 or more, the substitution degree of the acyl group having 8 or more carbon atoms is high, and the substitution degree of the acyl group having 3 to 7 carbon atoms is less than 1.2. In such a case, the brittleness deteriorates and desired characteristics cannot be obtained.

In the cellulose ester resin (B) of the present invention, the total substitution degree (T) is 2.0 to 3.0, and the substitution degree of the acyl group having 3 to 7 carbon atoms is 1.2 to 3. If it is 0.0, there is no problem, but the total degree of substitution of acyl groups other than those having 3 to 7 carbon atoms, that is, acetyl groups or acyl groups having 8 or more carbon atoms, is preferably 1.3 or less.

Further, the total substitution degree (T) of the acyl group of the cellulose ester resin (B) is more preferably in the range of 2.5 to 3.0.

The cellulose ester resin (B) of the present invention is preferably at least one selected from cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate benzoate, cellulose propionate, and cellulose butyrate, that is, carbon Those having an acyl group having 3 or 4 atoms as a substituent are preferred.

Among these, particularly preferable cellulose ester resins are cellulose acetate propionate and cellulose propionate.

The portion not substituted with an acyl group usually exists as a hydroxyl group. These can be synthesized by known methods.

Incidentally, the substitution degree of the acetyl group and the substitution degree of other acyl groups were determined by the method prescribed in ASTM-D817-96.

The weight average molecular weight (Mw) of the cellulose ester resin of the present invention is 75,000 or more, particularly from the viewpoint of improving compatibility with the acrylic resin (A) and brittleness, and is preferably in the range of 75,000 to 300,000. More preferably, it is within the range of 240000, particularly preferably from 160000 to 240000.

When the weight average molecular weight (Mw) of the cellulose ester resin is less than 75,000, the heat resistance and brittleness improvement effects are not sufficient, and the effects of the present invention cannot be obtained. In the present invention, two or more kinds of cellulose resins can be mixed and used.

The weight average molecular weight of the cellulose ester resin of the present invention can be measured by the GPC.
<Acrylic resin (A) and cellulose ester resin (B)>
In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably contained in a compatible state at a mass ratio of 95: 5 to 50:50, preferably 70:30. ~ 60: 40.

If the mass ratio of the acrylic resin (A) and the cellulose ester resin (B) is more than 95: 5, the effect of the cellulose ester resin (B) cannot be sufficiently obtained, and the mass ratio is When the amount of acrylic resin is less than 50:50, the photoelastic coefficient is increased.

In the optical film of the present invention, the acrylic resin (A) and the cellulose ester resin (B) are preferably contained in a compatible state. The physical properties and quality required for an optical film are achieved by supplementing each other by dissolving different resins.

Whether the acrylic resin (A) and the cellulose ester resin (B) are in a compatible state can be determined by, for example, the glass transition temperature Tg.

For example, when the two resins have different glass transition temperatures, when the two resins are mixed, there are two or more glass transition temperatures for each resin because there is a glass transition temperature for each resin. When they are compatible, the glass transition temperature specific to each resin disappears and becomes one glass transition temperature, which is the glass transition temperature of the compatible resin.

The glass transition temperature referred to here is an intermediate value determined according to JIS K7121 (1987) using a differential scanning calorimeter (DSC-7 model manufactured by Perkin Elmer) at a heating rate of 20 ° C./min. The point glass transition temperature (Tmg).

In the optical film of the present invention, the weight average molecular weight (Mw) of the acrylic resin (A), the weight average molecular weight (Mw) of the cellulose ester resin (B), and the degree of substitution are different in solubility in the solvent of both resins. It is obtained by measuring each after use.

When fractionating the resin, it is possible to extract and separate the soluble resin by adding a compatible resin in a solvent that is soluble only in either one. At this time, heating operation or reflux is performed. May be.

The resin may be separated by combining two or more of these solvent combinations. The dissolved resin and the resin remaining as an insoluble matter are filtered off, and the solution containing the extract can be separated by an operation of evaporating the solvent and drying.

These fractionated resins can be identified by general structural analysis of polymers. When the optical film of the present invention contains a resin other than the acrylic resin (A) and the cellulose ester resin (B), it can be separated by the same method.

If the weight average molecular weights (Mw) of the compatible resins are different, the high molecular weight substances are eluted earlier by gel permeation chromatography (GPC), and the lower molecular weight substances are eluted after a longer time. Therefore, it can be easily fractionated and the molecular weight can be measured.

In addition, the molecular weight of the compatible resin is measured by GPC, and at the same time, the resin solution eluted every time is separated, the solvent is distilled off, and the dried resin is different by quantitatively analyzing the structure. By detecting the resin composition for each molecular weight fraction, it is possible to identify each compatible resin.

It is also possible to detect each of the compatible resins by measuring the molecular weight distribution of each of the resins separated in advance by the difference in solubility in a solvent by GPC.

The total mass of the acrylic resin (A) and the cellulose ester resin (B) in the optical film of the present invention is preferably 55% by mass or more of the optical film, more preferably 60% by mass or more, and particularly preferably 70% by mass or more.
<Other additive resins>
When the resin other than the acrylic resin (A) and the cellulose ester resin (B) is used for the optical film of the present invention, it is preferable to adjust the addition amount within a range that does not impair the function of the optical film of the present invention.

A preferred resin is a low molecular acrylic resin obtained by polymerizing an ethylenically unsaturated monomer described in paragraphs (0072) to (0123) of JP 2010-32655 A (weight average molecular weight Mw is 500 or more and 30000 or less). Polymer).

Particularly preferably, Mw is 2000 to 10,000. If it is 1000 or less, a problem occurs in bleed-out, and if it exceeds 30000, the transparency deteriorates.

Also, a vinyl polymer having an amide bond described in Japanese Patent No. 4138654 can be used.

The low molecular acrylic resin of the present invention and the vinyl polymer having an amide bond are 0 to 15% by mass, preferably 0 to 10% by mass, based on the total mass of the optical film.
<Acrylic particles (D)>
The optical film of the present invention may contain acrylic particles (D) described in Patent Document 1.

Examples of such commercially available multilayered acrylic granular composites include, for example, “Metablene” manufactured by Mitsubishi Rayon Co., “Kane Ace” manufactured by Kaneka Chemical Co., Ltd., “Paralloid” manufactured by Kureha Chemical Co., Ltd., Rohm and Haas “Acryloid” manufactured by KK, “Staffyroid” manufactured by Ganz Kasei Kogyo Co., Ltd., “Parapet SA” manufactured by Kuraray Co., Ltd., and the like can be used alone or in combination of two or more.

Examples of commercial products of such a multilayer structure acrylic granular composite include, for example, “Metablene W-341” manufactured by Mitsubishi Rayon Co., Ltd., “Kaneace” manufactured by Kaneka Chemical Co., Ltd., “Paraloid” manufactured by Kureha Chemical Co., Ltd., Examples include "Acryloid" manufactured by Rohm and Haas, "Staffroid" manufactured by Gantz Kasei Kogyo, Chemisnow MR-2G, MS-300X (manufactured by Soken Chemical Co., Ltd.), and "Parapet SA" manufactured by Kuraray Co., Ltd. These can be used alone or in combination of two or more.

The optical film of the present invention preferably contains 0 to 30% by mass of acrylic particles (D) with respect to the total mass of the resin constituting the film, and is contained in the range of 1.0 to 15% by mass. More preferably.
<Other additives>
The optical film of the present invention includes a retardation control agent for controlling retardation, a plasticizer for imparting processability to the film, an antioxidant for preventing deterioration of the film, and an ultraviolet ray for imparting an ultraviolet absorbing function. It is preferable to contain additives such as fine particles (matting agent) that impart slipperiness to the absorbent and film.

<Polyester polyol of glycol and dibasic acid>
Examples of the polyester polyol that can be used in the present invention include a dehydration condensation reaction between a glycol having an average carbon number of 2 to 3.5 and a dibasic acid having an average carbon number of 4 to 5.5, or the glycol. It is preferably one produced by a conventional method by addition of a dibasic anhydride having an average carbon number of 4 to 5.5 and a dehydration condensation reaction.

<Polyester of aromatic dicarboxylic acid and alkylene glycol>
As the retardation control agent of the present invention, an aromatic terminal polyester represented by the following general formula (I) can be used.

Formula (I) B- (GA) nGB
[Wherein, B is a benzene monocarboxylic acid residue, G is an alkylene glycol residue having 2 to 12 carbon atoms, an aryl glycol residue having 6 to 12 carbon atoms, or an oxyalkylene glycol residue having 4 to 12 carbon atoms, A represents an alkylene dicarboxylic acid residue having 4 to 12 carbon atoms or an aryl dicarboxylic acid residue having 6 to 12 carbon atoms, and n represents an integer of 1 or more. ]
In the general formula (I), a benzene monocarboxylic acid residue represented by B and an alkylene glycol residue, oxyalkylene glycol residue or aryl glycol residue represented by G, an alkylene dicarboxylic acid residue or aryl dicarboxylic group represented by A It is composed of an acid residue and can be obtained by a reaction similar to that of ordinary polyester.

Specific examples of the aromatic terminal polyester of the present invention include paragraphs (0183) to (0186) of JP-A 2010-32655.

The content of the aromatic terminal polyester of the present invention is preferably 0 to 20% by mass, more preferably 1 to 11% by mass in the optical film.

<Polyhydric ester compound>
The optical film of the present invention can contain a polyhydric alcohol ester compound.

Examples of the polyhydric alcohol ester compound include paragraphs (0218) to (0170) of JP-A 2010-32655.

<Sugar ester compound>
As the sugar ester compound of the present invention, it is possible to use a sugar ester compound having at least one pyranose structure or at least one furanose structure and esterifying all or part of the OH groups of the structure. preferable.

Examples of the sugar ester compound used in the present invention include glucose, galactose, mannose, fructose, xylose, arabinose, lactose, sucrose, cellobiose, cellotriose, maltotriose, raffinose, etc. What has is preferable. An example is sucrose.

The sugar ester compound used in the present invention is one in which part or all of the hydroxyl groups of the sugar compound are esterified or a mixture thereof.

Specific examples of the sugar ester compound of the present invention include paragraphs (0060) to (0070) of JP-A 2010-32655.

<Other additives>
In the optical film of the present invention, a plasticizer, a retardation control agent, an antioxidant, an ultraviolet absorber, matte particles, and the like can be used in combination.

Examples of the plasticizer include phthalate ester, fatty acid ester, trimellitic ester, phosphate ester, polyester, and epoxy.

For phosphate plasticizers, triphenyl phosphate, tricresyl phosphate, cresyl diphenyl phosphate, octyl diphenyl phosphate, diphenylbiphenyl phosphate, trioctyl phosphate, tributyl phosphate, etc. For phthalate ester plasticizers, diethyl phthalate, dimethoxy Ethyl phthalate, dimethyl phthalate, dioctyl phthalate, dibutyl phthalate, di-2-ethylhexyl phthalate and the like can be used.

Of these, polyester-based and phthalate-based plasticizers are preferably used. Polyester plasticizers are superior in non-migration and extraction resistance compared to phthalate ester plasticizers such as dioctyl phthalate, but are slightly inferior in plasticizing effect and compatibility.

Therefore, it can be applied to a wide range of uses by selecting or using these plasticizers according to the use.

The polyester plasticizer is a reaction product of a monovalent or tetravalent carboxylic acid and a monovalent or hexavalent alcohol, and is mainly obtained by reacting a divalent carboxylic acid with a glycol. . Representative divalent carboxylic acids include glutaric acid, itaconic acid, adipic acid, phthalic acid, azelaic acid, sebacic acid and the like.

In particular, when adipic acid, phthalic acid, or the like is used, those having excellent plasticizing properties can be obtained. Examples of the glycol include glycols such as ethylene, propylene, 1,3-butylene, 1,4-butylene, 1,6-hexamethylene, neopentylene, diethylene, triethylene, and dipropylene. These divalent carboxylic acids and glycols may be used alone or in combination.

The ester plasticizer may be any of ester, oligoester and polyester types, and the molecular weight is preferably in the range of 100 to 10000, but preferably in the range of 600 to 3000, the plasticizing effect is large.

Also, the viscosity of the plasticizer has a correlation with the molecular structure and molecular weight, but in the case of an adipic acid plasticizer, the range of 200 to 5000 mPa · s (25 ° C.) is preferable because of compatibility and plasticization efficiency. Furthermore, some polyester plasticizers may be used in combination.

The plasticizer is preferably added in an amount of 0.5 to 30 parts by mass with respect to 100 parts by mass of the composition containing an acrylic resin. If the added amount of the plasticizer exceeds 30 parts by mass, the surface becomes sticky, which is not preferable for practical use. These plasticizers may be used alone or in combination of two or more.

<Phase difference control agent>
As the phase difference controlling agent of the present invention, those containing bisphenol A in the molecule are also preferred. A compound in which ethylene oxide or propylene oxide is added to both ends of bisphenol A can be used.

For example, BP series such as New Paul BP-2P, BP-3P, BP-23P, BP-5P, BPE-20 (F), BPE-20NK, BPE-20T, BPE-40, BPE-60, BPE-100, There are BPE series (manufactured by Sanyo Chemical Co., Ltd.) such as BPE-180, and BPX series (manufactured by ADEKA Corporation) such as Adeka polyether BPX-11, BPX-33, BPX-55.

Diallyl bisphenol A, dimethallyl bisphenol A, tetrabromobisphenol A in which bisphenol A is substituted with bromine, oligomers and polymers obtained by polymerizing this, bisphenol A bis (diphenyl phosphate) substituted with diphenyl phosphate, etc. Can be used.

Polycarbonate obtained by polymerizing bisphenol A, polyarylate obtained by polymerizing bisphenol A with a dibasic acid such as terephthalic acid, and an epoxy oligomer or polymer polymerized with an epoxy-containing monomer can also be used.

Modiper CL130D or L440-G obtained by graft polymerization of bisphenol A and styrene or styrene acrylic can also be used.

Also preferred are those having a triazine structure. The compounds described in JP-A-2001-166144 can be used.

<Antioxidant>
In this invention, what is generally known can be used as an antioxidant. In particular, lactone, sulfur, phenol, double bond, hindered amine, and phosphorus compounds can be preferably used.

For example, those including those commercially available from BASF Japan under the trade names “IrgafosXP40” and “IrgafosXP60” are preferable.

The phenolic compound preferably has a 2,6-dialkylphenol structure. For example, BASF Japan Ltd., “Irganox 1076”, “Irganox 1010”, ADEKA Corporation “ADEKA STAB AO-50” are commercially available. What is done is preferable.

The phosphorous compounds are, for example, from Sumitomo Chemical Co., Ltd., “Sumilizer GP”, ADEKA Co., Ltd., ADK STAB PEP-24G, “ADK STAB PEP-36” and “ADK STAB 3010”, from BASF Japan Co., Ltd., “IRGAFOS” P-EPQ "and those commercially available from Sakai Chemical Industry Co., Ltd. under the trade name" GSY-P101 "are preferred.

The hindered amine compound is preferably commercially available, for example, from BASF Japan Co., Ltd. under the trade names “Tinuvin 144” and “Tinvin 770” and from ADEKA Co., Ltd. under the name “ADK STAB LA-52”.

The above sulfur compounds are preferably those commercially available from Sumitomo Chemical Co., Ltd. under the trade names “Sumilizer TPL-R” and “Sumilizer TP-D”.

The above-mentioned double bond compound is preferably commercially available from Sumitomo Chemical Co., Ltd. under the trade names of “Sumilizer GM” and “Sumilizer GS”.

Furthermore, it is possible to contain a compound having an epoxy group as described in US Pat. No. 4,137,201 as an acid scavenger.

The amount of these antioxidants and the like to be added is appropriately determined in accordance with the process for recycling and use, but generally 0.05 to 20% by mass, preferably with respect to the resin as the main raw material of the film Is added in the range of 0.1 to 1% by mass.

These antioxidants can obtain a synergistic effect by using several different types of compounds in combination rather than using only one kind. For example, the combined use of lactone, phosphorus, phenol and double bond compounds is preferred.

<Colorant>
In the present invention, it is preferable to use a colorant. The colorant means a dye or a pigment. In the present invention, the colorant refers to a colorant having an effect of making the color tone of a liquid crystal screen a blue tone, adjusting a yellow index, and reducing haze.

Various dyes and pigments can be used as the colorant, but anthraquinone dyes, azo dyes, phthalocyanine pigments and the like are effective.

<Ultraviolet absorber>
Although the ultraviolet absorber used in the present invention is not particularly limited, for example, oxybenzophenone compounds, benzotriazole compounds, salicylic acid ester compounds, benzophenone compounds, cyanoacrylate compounds, triazine compounds, nickel complex compounds, inorganic powders Examples include the body. It is good also as a polymer type ultraviolet absorber.

<Matting agent>
In the present invention, it is preferable to add a matting agent in order to impart film slipperiness.

The matting agent used in the present invention may be either an inorganic compound or an organic compound as long as it does not impair the transparency of the obtained film and has heat resistance during melting. These matting agents can be used alone or in combination of two or more.

High transparency and slipperiness can be achieved at the same time by using particles having different particle sizes and shapes (for example, needle shape and spherical shape).

Among these, silicon dioxide is particularly preferably used since it has a refractive index close to that of cellulose ester and is excellent in transparency (haze).

Specific examples of silicon dioxide include Aerosil 200V, Aerosil R972V, Aerosil R972, R974, R812, 200, 300, R202, OX50, TT600, NAX50 (manufactured by Nippon Aerosil Co., Ltd.), Sea Hoster KEP-10, Sea Hoster KEP- 30, Seahoster KEP-50 (above, manufactured by Nippon Shokubai Co., Ltd.), Silo Hovic 100 (manufactured by Fuji Silysia), Nip Seal E220A (manufactured by Nippon Silica Kogyo), Admafine SO (manufactured by Admatechs), etc. Goods etc. can be preferably used.

The shape of the particles can be used without particular limitation, such as indefinite shape, needle shape, flat shape, spherical shape, etc. However, the use of spherical particles is preferable because the transparency of the resulting film can be improved.

When the particle size is close to the wavelength of visible light, light is scattered and the transparency is deteriorated. Therefore, the particle size is preferably smaller than the wavelength of visible light, and more preferably ½ or less of the wavelength of visible light. . If the size of the particles is too small, the slipperiness may not be improved, so the range of 80 nm to 180 nm is particularly preferable.

The particle size means the size of the aggregate when the particle is an aggregate of primary particles. Moreover, when a particle is not spherical, it means the diameter of a circle corresponding to the projected area.

<Viscosity reducing agent>
In the present invention, a hydrogen bonding solvent can be added for the purpose of reducing the melt viscosity.

Hydrogen-bonding solvent refers to J.I. N. As described in Israel Ativili, “Intermolecular Forces and Surface Forces” (Takeshi Kondo, Hiroyuki Oshima, Maglow Hill Publishing, 1991) and electrically negative atoms (oxygen, nitrogen, fluorine, chlorine) An organic solvent capable of producing a hydrogen atom-mediated “bond” that occurs between an electronegative atom and a covalently bonded hydrogen atom, that is, a bond having a large bonding moment and containing hydrogen, such as OH (Oxygen hydrogen bond), N—H (nitrogen hydrogen bond), FH (fluorine hydrogen bond), and an organic solvent that can arrange adjacent molecules.

These have the ability to form stronger hydrogen bonds with cellulose than intermolecular hydrogen bonds of cellulose resin. In the melt casting method performed in the present invention, the glass transition temperature of the cellulose resin used alone is higher than that. The melting temperature of the cellulose resin composition can be lowered by the addition of a hydrogen bonding solvent, or the melt viscosity of the cellulose resin composition containing a hydrogen bonding solvent can be lowered at the same melting temperature as the cellulose resin. .

(Physical properties of optical film)
Hereinafter, the characteristics of the optical film according to the present invention will be described.

<transparency>
As an index for judging the transparency of the optical film in the present invention, haze value (turbidity) is used.

In particular, liquid crystal display devices used outdoors are required to have sufficient brightness and high contrast even in a bright place. Therefore, the haze value is required to be 1.0% or less, and 0.5% or less. More preferably.

Further, the total light transmittance is preferably 90% or more, and more preferably 93% or more. Moreover, as a realistic upper limit, it is about 99%. In order to achieve excellent transparency expressed by such total light transmittance, it is necessary not to introduce additives and copolymerization components that absorb visible light, or to remove foreign substances in the polymer by high-precision filtration. It is effective to reduce the diffusion and absorption of light inside the film.

According to the optical film of the present invention containing the acrylic resin (A) and the cellulose ester resin (B), high transparency can be obtained, but when using acrylic particles for the purpose of improving another physical property, By reducing the difference in refractive index between the resin (acrylic resin (A) and cellulose ester resin (B)) and acrylic particles (D), an increase in haze value can be prevented.

In addition, the optical film of the present invention preferably has a defect with a diameter of 5 μm or more in the film plane of 1 piece / 10 cm square or less. More preferably, it is 0.5 piece / 10 cm square or less, more preferably 0.1 piece / 10 cm square or less.

Here, the diameter of the defect indicates the diameter when the defect is circular, and when it is not circular, the range of the defect is determined by observing with a microscope according to the following method, and the maximum diameter (diameter of circumscribed circle) is determined.

The range of the defect is the size of the shadow when the defect is observed with the transmitted light of the differential interference microscope when the defect is a bubble or a foreign object. When the defect is a change in the surface shape, such as transfer of a roll flaw or an abrasion, the size is confirmed by observing the defect with the reflected light of a differential interference microscope.

In addition, when observing with reflected light, if the size of the defect is not clear, aluminum or platinum is vapor-deposited on the surface for observation.

In order to obtain a film having excellent quality expressed by such a defect frequency with high productivity, it is necessary to filter the polymer solution with high precision immediately before casting, to increase the cleanliness around the casting machine, It is effective to set drying conditions after rolling stepwise and to dry efficiently while suppressing foaming.

When the number of defects is more than 1/10 cm square, for example, when a tension is applied to the film during processing in a later process, the film may be broken with the defect as a starting point and productivity may be reduced. Moreover, when the diameter of a defect becomes 5 micrometers or more, it can confirm visually by polarizing plate observation etc., and when used as an optical member, a bright spot may arise.

<Retardation>
For the retardation, a 35 mm × 35 mm sample was cut from the produced optical film, conditioned for 2 hours at 25 ° C. and 55% RH, and measured from the vertical direction at 590 nm with an automatic birefringence meter (KOBRA WR, Oji Scientific Co., Ltd.). Ro and Rt at each wavelength were calculated from the measured values and the extrapolated values of the retardation values measured in the same manner while tilting the film surface.

The optical film of the present invention has an in-plane retardation value Ro (590) defined by the following formula (I) in the range of 30 to 300 nm, and is a retarder in the thickness direction defined by the following formula (II). It is preferable to adjust so that the foundation value Rt (590) is in the range of 50 to 300 nm.
Formula (I): Ro (590) = (nx−ny) × d (nm)
Formula (II): Rt (590) = {(nx + ny) / 2−nz} × d (nm)
[In the above formula, Ro (590) represents the in-plane retardation value in the film at a wavelength of 590 nm, and Rt (590) represents the retardation value in the thickness direction in the film at 590 nm.

D represents the thickness (nm) of the optical film, nx represents the maximum refractive index in the plane of the film at 590 nm, and is also referred to as the refractive index in the slow axis direction. ny represents the refractive index in the direction perpendicular to the slow axis in the film plane at 590 nm, and nz represents the refractive index of the film in the thickness direction at 590 nm. ]
The in-plane retardation value Ro (590) is preferably in the range of 60 to 250 nm.

On the other hand, the retardation value Rt (590) in the thickness direction is preferably in the range of 60 to 250 nm.

For the desired retardation, the composition of the acrylic resin and the cellulose ester resin is adjusted within a mass ratio of 95: 5 to 50:50, and the ratio of each resin is adjusted. This is done by adjusting the amount to be added.

Furthermore, by adjusting and controlling the stretching temperature (combination of the temperatures of the respective sections), the magnification, the stretching speed, the stretching order, the residual solvent amount of the film when stretching, and the like according to the composition of the film. The retardation value can be set to a desired value.

By adjusting the retardation to such a range, the viewing angle of the liquid crystal display device using the film of the present invention can be widened and the front contrast can be improved.

Front contrast = (brightness of white display measured from normal direction of display device) / (brightness of black display measured from normal direction of display device)
The viewing angle is an angle at which a certain level of contrast can be maintained when the viewing direction of the liquid crystal display device is tilted from the normal direction.

The thickness of the optical film of the present invention is preferably 20 μm or more and 150 μm or less. More preferably, it is 30 μm or more and 80 μm or less.

The optical film of the present invention can be particularly preferably used as a polarizing plate protective film for a large-sized liquid crystal display device or a liquid crystal display device for outdoor use as long as the above physical properties are satisfied.
<Method for producing optical film>
The optical film of the present invention is preferably produced by a melt casting coextrusion film forming method from the viewpoint of flatness and thinning.
<Method for producing optical film by melt casting coextrusion film forming method>
The method for producing an optical film of the present invention is a method for producing an optical film in which at least an acrylic resin (A) and a cellulose ester resin (B) are melted and coextruded from a die and cast on a cooling roll.

Hereinafter, the whole manufacturing method will be described.

<Melted pellet manufacturing process>
The mixture of acrylic resin (A), cellulose ester (including cellulose ester resin (B)), plasticizer and other additives used for melt extrusion is usually preferably kneaded in advance and pelletized.

Pelletization may be performed by a known method. For example, dry acrylic resin (A), dry cellulose ester, plasticizer, and other additives are fed to an extruder with a feeder and kneaded using a single or twin screw extruder. Then, it can be extruded from a die into a strand, cooled with water or air, and cut.

It is important to dry the raw material before extruding to prevent the raw material from being decomposed. In particular, since cellulose ester easily absorbs moisture, it is preferable to dry it at 70 to 140 ° C. for 3 hours or more with a dehumidifying hot air dryer or a vacuum dryer so that the moisture content is 200 ppm or less, and further 100 ppm or less.

Additives may be fed into the extruder and fed into the extruder, or may be fed through individual feeders. A small amount of an additive such as an antioxidant is preferably mixed in advance in order to mix uniformly.

Mixing of the antioxidants may be performed by mixing solids, and if necessary, the antioxidant may be dissolved in a solvent and mixed by impregnating the acrylic resin (A) and cellulose ester, or You may spray and mix.

A vacuum nauter mixer or the like is preferable because drying and mixing can be performed simultaneously. Further, if the contact with air, such as the exit from the feeder unit or die, it is preferable that the atmosphere such as dehumidified air and dehumidified N ₂ gas.

The extruder is preferably processed at as low a temperature as possible so as to be able to be pelletized so that the shear force is suppressed and the resin does not deteriorate (molecular weight reduction, coloring, gel formation, etc.). For example, in the case of a twin screw extruder, it is preferable to rotate in the same direction using a deep groove type screw. From the uniformity of kneading, the meshing type is preferable.

Film formation is performed using the pellets obtained as described above. It is also possible to feed the raw material powder directly to the extruder with a feeder and form a film as it is without pelletization.

<Process for extruding molten mixture from die to cooling roll>
A line for introducing the acrylic resin (A) from the molten mixture to the casting die and a line for introducing the cellulose tellur resin from the molten mixture to the casting die are provided side by side, and each molten mixture is laminated in the casting die. .

First, the pellets produced are extruded using a single-screw or twin-screw extruder, the melting temperature Tm during extrusion is set to about 200 to 300 ° C., filtered through a leaf disk type filter or the like to remove foreign matter, and then the T-die The film is coextruded into a film, solidified on a cooling roll, and cast while pressing with an elastic touch roll.

When introducing into the extruder from the supply hopper, it is preferable to prevent oxidative decomposition or the like under vacuum, reduced pressure, or inert gas atmosphere. Tm is the temperature of the die exit portion of the extruder.

∙ If foreign matter such as scratches or plasticizer aggregates adheres to the die, streaky defects may occur. Such a defect is also called a die line, but in order to reduce surface defects such as the die line, it is preferable to have a structure in which the resin retention portion is minimized in the piping from the extruder to the die. . It is preferable to use a die that has as few scratches as possible inside the lip.

The inner surface that comes into contact with the molten resin, such as an extruder or a die, is preferably subjected to surface processing that makes it difficult for the molten resin to adhere to the surface by reducing the surface roughness or using a material with low surface energy. Specifically, a hard chrome plated or ceramic sprayed material is polished so that the surface roughness is 0.2 S or less.

The cooling roll of the present invention is not particularly limited, but is a roll having a structure in which a heat medium or a coolant that can be controlled in temperature flows through a highly rigid metal roll, and the size is not limited. It is sufficient that the film is large enough to cool the film, and the diameter of the cooling roll is usually about 100 mm to 1 m.

The surface material of the cooling roll includes carbon steel, stainless steel, aluminum, titanium and the like. Further, in order to increase the surface hardness or improve the releasability from the resin, it is preferable to perform a surface treatment such as hard chrome plating, nickel plating, amorphous chrome plating, or ceramic spraying.

The surface roughness of the cooling roll surface is preferably 0.1 μm or less in terms of Ra, and more preferably 0.05 μm or less. The smoother the roll surface, the smoother the surface of the resulting film. Of course, it is preferable that the surface processed is further polished to have the above-described surface roughness.

Examples of the elastic touch roll of the present invention include JP-A-03-124425, JP-A-08-224772, JP-A-07-1000096, JP-A-10-272676, WO97-028950, JP-A-11-235747, JP-A-11-235747. As described in JP 2002-36332 A, JP 2005-172940 A, and JP 2005-280217 A, a thin-film metal sleeve-covered silicon rubber roll can be used.

When peeling the film from the cooling roll, it is preferable to control the tension to prevent deformation of the film.

<Extension process>
In the present invention, it is preferable that the film obtained as described above is further stretched 1.01 to 3.0 times in at least one direction after passing through the step of contacting the cooling roll. The sharpness of the streaks becomes gentle by stretching and can be highly corrected.

Preferably, the film is stretched 1.1 to 2.0 times in both the longitudinal (film transport direction) and lateral (width direction) directions.

As the stretching method, a known roll stretching machine or tenter can be preferably used. In particular, in the case where the optical film is a retardation film that also serves as a polarizing plate protective film, it is preferable to stack the polarizing film in a roll form by setting the stretching direction to the width direction.

Usually, the draw ratio is 1.1 to 3.0 times, preferably 1.2 to 1.5 times, and the draw temperature is usually Tg to Tg + 50 ° C. of the resin constituting the film, preferably Tg to Tg + 40 ° C. Performed in the temperature range.

The stretching is preferably performed under a uniform temperature distribution controlled in the width direction. The temperature is preferably within ± 2 ° C, more preferably within ± 1 ° C, and particularly preferably within ± 0.5 ° C.

The film may be contracted in the longitudinal direction or the lateral direction for the purpose of adjusting the retardation of the optical film produced by the above method and reducing the dimensional change rate.

In order to shrink in the longitudinal direction, for example, there is a method in which the film is shrunk by temporarily clipping out the width stretching and relaxing in the longitudinal direction, or by gradually narrowing the interval between adjacent clips of the transverse stretching machine.

In-plane retardation (Ro) and thickness direction retardation (Rt) of the optical film of the present invention can be adjusted as appropriate, but Ro is preferably 0 to 200 nm and Rt is preferably −150 to 400 nm.

In addition, when the refractive index Nx in the slow axis direction of the film, the refractive index Ny in the fast axis direction, the refractive index Nz in the thickness direction, and the film thickness of the film are d (nm),
Ro = (Nx−Ny) × d
Rt = {(Nx + Ny) / 2−Nz} × d
Represented as: (Measurement wavelength 590nm)
The variation in retardation is preferably as small as possible, and is usually within ± 10 nm, preferably ± 5 nm or less, and more preferably ± 2 nm or less.

Uniformity in the slow axis direction is also important, and the angle is preferably −5 to + 5 ° with respect to the film width direction, more preferably in the range of −1 to + 1 °, particularly −0. A range of 5 to + 0.5 ° is preferable, and a range of −0.1 to + 0.1 ° is particularly preferable. These variations can be achieved by optimizing the stretching conditions.

In the optical film of the present invention, it is preferable that the height from the top of the adjacent mountain to the bottom of the valley is 300 nm or more, and there is no streak continuous in the longitudinal direction with an inclination of 300 nm / mm or more.

The shape of the streak was measured using a surface roughness meter. Specifically, using a Mitutoyo SV-3100S4, a stylus (diamond needle) having a tip shape of 60 ° cone and a tip curvature radius of 2 μm was used. The film is scanned in the width direction of the film at a measurement speed of 1.0 mm / sec while applying a load of 0.75 mN, and a cross-sectional curve is measured with a Z-axis (thickness direction) resolution of 0.001 μm.

From this curve, the height of the streak reads the vertical distance (H) from the top of the mountain to the bottom of the valley. The slope of the streak is obtained by reading the horizontal distance (L) from the top of the mountain to the bottom of the valley and dividing the vertical distance (H) by the horizontal distance (L).

Since the optical film of the present invention is produced by the melt casting coextrusion film forming method, the amount of the solvent contained is 0.01% by mass or less when wound up as a roll film. The amount of the solvent can be measured by a usual method.

The return material is a product obtained by finely pulverizing the optical film, which is generated when the optical film is formed, and is obtained by cutting off both sides of the film, or by using an optical film original that has been speculated out due to scratches, etc. .

Also, an acrylic resin, a cellulose ester resin, and in some cases, acrylic particles kneaded into pellets can be preferably used.

The optical film of the present invention is preferably a film. Specifically, the optical film shows a thickness of about 100 m to 5000 m, and is usually in the form of a roll.

The film width is preferably 1.3 to 4 m, more preferably 1.4 to 2 m.

The film thickness of the optical film of the present invention is not particularly limited, but when used for a polarizing plate protective film described later, it is preferably 20 to 200 μm, more preferably 25 to 100 μm, and 30 to 80 μm. It is particularly preferred.
<Polarizing plate>
When using the optical film of this invention as a protective film for polarizing plates, a polarizing plate can be produced by a general method.

It is preferable that an adhesive layer is provided on the back side of the optical film of the present invention, and is bonded to at least one surface of a polarizer produced by immersion and stretching in an iodine solution.

On the other surface, the optical film of the present invention may be used, or another polarizing plate protective film may be used. For example, a commercially available cellulose ester film (for example, Konica Minoltack KC8UX, KC4UX, KC5UX, KC8UY, KC4UY, KC12UR, KC8UCR-3, KC8UCR-4, KC8UCR-5, KC8UE, KC4FR-4, KC4FR-3, KC4FR-3, KC4FR-4 -1, KC8UY-HA, KC8UX-RHA, manufactured by Konica Minolta Opto Co., Ltd.) and the like are preferably used.

A polarizer, which is a main component of a polarizing plate, is an element that allows only light of a plane of polarization in a certain direction to pass. A typical polarizer currently known is a polyvinyl alcohol-based polarizing film, which is polyvinyl alcohol. There are one in which iodine is dyed on a system film and one in which dichroic dye is dyed.

The polarizer is formed by forming a polyvinyl alcohol aqueous solution into a film and dyeing the film by uniaxial stretching or dyeing or uniaxially stretching, and then performing a durability treatment with a boron compound.

As the pressure-sensitive adhesive used in the pressure-sensitive adhesive layer, a pressure-sensitive adhesive having a storage elastic modulus at 25 ° C. in the range of 1.0 × 10 ⁴ Pa to 1.0 × 10 ⁹ Pa in at least a part of the pressure-sensitive adhesive layer is used. It is preferable to use a curable pressure-sensitive adhesive that forms a high molecular weight body or a crosslinked structure by various chemical reactions after the pressure-sensitive adhesive is applied and bonded.

Specific examples include, for example, urethane adhesives, epoxy adhesives, aqueous polymer-isocyanate adhesives, curable adhesives such as thermosetting acrylic adhesives, moisture-curing urethane adhesives, polyether methacrylate types, Examples include anaerobic pressure-sensitive adhesives such as ester-based methacrylate type and oxidized polyether methacrylate, cyanoacrylate-based instantaneous pressure-sensitive adhesives, and acrylate-peroxide-based two-component instantaneous pressure-sensitive adhesives.

The above-mentioned pressure-sensitive adhesive may be a one-component type or a type in which two or more components are mixed before use.

The pressure-sensitive adhesive may be a solvent system using an organic solvent as a medium, or an aqueous system such as an emulsion type, a colloidal dispersion type, or an aqueous solution type that is a medium containing water as a main component. It may be a solvent type. The concentration of the pressure-sensitive adhesive liquid may be appropriately determined depending on the film thickness after adhesion, the coating method, the coating conditions, and the like, and is usually 0.1 to 50% by mass.
<Liquid crystal display device>
By incorporating the polarizing plate bonded with the optical film of the present invention into a liquid crystal display device, it is possible to produce various liquid crystal display devices with excellent visibility, but particularly outdoors such as large liquid crystal display devices and digital signage. It is preferably used for a liquid crystal display device for use. The polarizing plate of the present invention is bonded to a liquid crystal cell via the adhesive layer or the like.

The polarizing plate of the present invention includes various types such as a reflective type, a transmissive type, a transflective type LCD, a TN type, an STN type, an OCB type, a HAN type, a VA type (PVA type, MVA type), and an IPS type (including an FFS type). It is preferably used in a drive type LCD. In particular, in a large-screen display device with a VA screen of 30 or more, particularly 30 to 54 screens, the effect is maintained for a long time without white spots at the periphery of the screen.

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
Example 1
EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Acrylic resins A-1 to A-82 in Tables 1 and 2 were produced by a known method. In the table, N-ACEHPI is N-acryloyloxyethylhexahydrophthalimide, THFAC is tetrahydrofluoroacrylate, BRAC is γ-butyrolactone acrylate, MTEGAC is methoxytriethylene glycol acrylate, and ACOES is 2-acryloyloxyethyl succinate. MACOES is 2-methacryloyloxyethyl succinate, DMAMEMAC is dimethylaminoethyl methacrylate, TMPMAC is tetramethylpiperidine methacrylate, ACMO is acryloylmorpholine, and HEMA is hydroxyethyl methacrylate.

<Creation of optical film sample>
The following materials were further dried while mixing at 80 ° C. and 1 Torr for 3 hours with a vacuum nauter mixer, and the resulting mixture was melt-mixed at 235 ° C. using a twin-screw extruder to be pelletized.

Acrylic resin A-1 (dried at 90 ° C for 3 hours and water content 1000ppm)
70 parts by mass Cellulose ester resin (cellulose acetate propionate: acyl group total substitution degree 2.75, acetyl group substitution degree 0.19, propionyl group substitution degree 2.56, Mw = 200000, dried at 100 ° C. for 3 hours and moisture 500 ppm) 30 parts by weight Tinuvin 928 (manufactured by BASF Japan) 1.1 parts by weight GSY-P101 (manufactured by Sakai Chemical Industry Co., Ltd.) 0.25 parts by weight Irganox 1010 (manufactured by BASF Japan) 0.5 parts by weight Part Sumilizer GS (manufactured by Sumitomo Chemical Co., Ltd.) 0.24 parts by mass Aerosil NAX50 (manufactured by Nippon Aerosil Co., Ltd.) 0.2 parts by mass Seahoster KEP-30 (manufactured by Nippon Shokubai Co., Ltd.) 0.02 parts by mass were obtained. Circulate the pellets with 70 ° C dehumidified air for more than 5 hours. Then, it was introduced into a single-screw extruder in the next step while maintaining a temperature of 100 ° C. A small amount of the pellet was taken out and the water content was measured and found to be 120 ppm.

The cellulose ester film was produced using the production apparatus shown in FIG.

The above pellets were melt extruded from a T die onto a first cooling roll having a surface temperature of 90 ° C. at a melting temperature of 240 ° C. using a single screw extruder to obtain a 120 μm cast film. At this time, the film was pressed on the first cooling roll with an elastic touch roll having a 2 mm thick metal surface.

First, the obtained film was stretched 60% in the transport direction at 175 ° C. by a stretching machine using a difference in peripheral speed of the roll. Next, it is introduced into a tenter having a preheating zone, a stretching zone, a holding zone, and a cooling zone (there is also a neutral zone for ensuring thermal insulation between the zones), and is 70 ° C. at 175 ° C. in the width direction. The film was cooled to 30 ° C., then released from the clip, and the clip gripping part was cut off to obtain an optical film sample 1 having a film thickness of 40 μm and a film width of 2500 mm.

Similarly, acrylic resin A and cellulose ester resin B were mixed as shown in Table 3 to prepare optical film samples 2 to 139.

In Samples 132 and 133, 5 parts by mass of 70 parts by mass of the acrylic resin were replaced with acrylic resin particle Methrene W-341 (manufactured by Mitsubishi Rayon Co., Ltd.).

Samples 16, 31, 39, 47, 55, 63, 71, 79, 89, 94, 99 had high melt viscosity, and it was difficult to obtain a cast film by melt extrusion.

Since the melt viscosity of Samples 116 and 131 was high, the flatness of the obtained cast film was slightly poor when the melt temperature was set high.

The melting temperature was set for each resin mixture as a temperature at which the melt viscosity becomes 1000 Pa · s.
<Evaluation of optical film sample>
All evaluations were performed in an atmosphere of 23 ° C. and 55% RH unless otherwise specified. The sample used was stored in advance in the same atmosphere for 24 hours. The results are shown in the table. In the table, ac represents an acetyl group, and pr represents a propionyl group.

(Heat resistance evaluation (haze and dimensional change after cycle thermo))
The heat resistance of the optical film was evaluated as follows by the haze and dimensional change after the cycle thermo. It can be determined that the lower the haze after cycle thermostat is, the more chemically stable and the higher the heat resistance. Moreover, it can be judged that physical heat resistance is so excellent that there are few dimensional changes.

(Cycle thermo condition)
The optical film was processed according to the environmental test method ED-2531B of the liquid crystal display device.

The low temperature side was -35 ° C for 3 hours and the high temperature side was 90 ° C for 3 hours, and this was repeated 10 cycles.

<Haze%>
One optical film sample treated under the above cycle thermo conditions was measured using a haze meter (NDH2000 type, manufactured by Nippon Denshoku Industries Co., Ltd.) according to JIS K-7136.

<Dimensional change%>
The mark (cross) was marked with two cutters in the casting direction of the optical film, the cycle thermo treatment was performed, the distance between the mark (cross) before and after treatment was measured with an optical microscope, and evaluated according to the following criteria: .

Dimensional change (%) = [(a1-a2) / a1] × 100
In the formula, a1 represents a distance before the cycle thermo processing, and a2 represents a distance after the cycle thermo processing.

<Brittleness evaluation>
The optical film sample was punched into a circular hole with a punch, and the shape of the cut was visually observed. Judgment was made based on the following criteria.

○: A beautifully round hole is opened. Δ: There is a slight crack at the cut. ×: A crack with a length of more than half of the hole diameter is formed.
<Preparation of polarizing plate>
Using the optical film samples 1 to 133 prepared as described above, the alkali saponification treatment described below was performed to prepare a polarizing plate.

<Alkali saponification treatment>
Saponification process 2M-NaOH 50 ° C. 90 seconds Water washing process Water 30 ° C. 45 seconds Neutralization process 10% HCl 30 ° C. 45 seconds Water washing process Water 30 ° C. 45 seconds After saponification treatment, water washing, neutralization, water washing are performed in this order. Subsequently, it dried at 80 degreeC.

<Production of polarizer>
A 120 μm-thick long roll polyvinyl alcohol film was immersed in 100 parts by mass of an aqueous solution containing 1 part by mass of iodine and 4 parts by mass of boric acid, and stretched 6 times at 50 ° C. in the transport direction to produce a polarizer.

The KC4UY manufactured by Konica Minolta Opto Co., Ltd. was similarly saponified on one side of the polarizer, and the optical film sample of the present invention subjected to the alkali saponification treatment was bonded to the opposite side with a completely saponified polyvinyl alcohol 5% aqueous solution. As the agent, the polarizer was bonded to each other so that the transmission axis of the polarizer and the in-plane slow axis of the film were parallel, and dried to prepare a polarizing plate.

<Polarizing plate properties (adhesion evaluation)>
The adhesiveness of the prepared polarizing plate was evaluated as follows.

The polarizing plate was cut into rectangles, the optical film and the polarizer were peeled off while squeezing the corners by hand, and ranking was performed according to how they were peeled off.
1: The optical film and the polarizer can be peeled off easily 2: Can be peeled off by creating a trigger 3: The optical film can be peeled into small pieces 4: The optical film can be easily broken and cannot be peeled off, and the small pieces 5: The part that can be peeled is mixed 5: The optical film is torn immediately and cannot be peeled off <Production of liquid crystal display device>
The obtained polarizing plate was carefully peeled off from the viewing side polarizing plate previously bonded to the liquid crystal display device Wooo W32L-H90 manufactured by Hitachi, Ltd., which is an IPS type liquid crystal display device, and transmitted through the polarizing plate originally applied. In accordance with the axis, a polarizing plate was attached so that the optical film of the present invention produced through an adhesive was on the viewing side, and a liquid crystal display device was produced.

<Evaluation of screen unevenness>
Thereafter, in an environment of 23 ° C. and 55% RH, the backlight was continuously turned on for 1000 hours, the entire black display state was visually observed in a dark room, and the screen unevenness was visually sensory evaluated. The results are shown in the table.

◎: Unevenness is not observed at all in the bright room and darkroom ○: Not observed at all in the brightroom, but some unevenness is observed in the darkroom △: Not noticeable in the brightroom, but unevenness is observed in the darkroom ×: Bright Unevenness is observed in the room

When the optical film sample of the present invention was used, it was confirmed that the screen unevenness was greatly improved.

DESCRIPTION OF SYMBOLS 1 Extruder 2 Filter 3 Static mixer 4 Casting die 5 Rotating support body (1st cooling roll)
6 Nipping pressure rotating body (touch roll)
7 Rotating support (second cooling roll)
8 Rotating support (3rd cooling roll)
9, 11, 13, 14, 15 Transport roll 10 Optical film 12 Stretcher (tenter)
16 Winding device F Rolled film

Claims (5)

1. In an optical film containing an acrylic resin (A) and a cellulose ester resin (B) in a mass ratio of 95: 5 to 50:50, the acrylic resin (A) is represented by the following general formula (1), and has a weight average molecular weight. Mw is 20000 or more and 1000000 or less, The optical film characterized by the above-mentioned.
   General formula (1)
   -(MMA) p- (X) q- (Y) r-
   [Wherein, MMA is copolymerized with methyl methacrylate, X is copolymerized with MMA having at least one group selected from hydroxyl group, secondary amino group, tertiary amino group, phthalimide group, α, β-saturated ester group and ether group] Y represents a monomer unit that can be copolymerized with MMA and X. p, q, and r are% by mass, and 50 ≦ p ≦ 99, 1 ≦ q ≦ 50, and p + q + r = 100. ]
2. 2. The total substitution degree (T) of the acyl group of the cellulose ester resin (B) is 2.0 or more and 3.0 or less, and the substitution degree of the acyl group having 3 or more and 7 or less carbon atoms is 1.2 or more. 2. The optical film according to claim 1, wherein the cellulose ester resin (B) has a weight average molecular weight Mw of 75,000 or more and 300,000 or less.
3. The said optical film contains acrylic particle (D) of 0.5 mass% or more and 30 mass% or less with respect to the total mass of resin which comprises this optical film, The Claim 1 or 2 characterized by the above-mentioned. The optical film as described.
4. A polarizing plate comprising the optical film according to any one of claims 1 to 3.
5. A liquid crystal display device comprising the optical film according to any one of claims 1 to 3.

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